Decryption of a ciphertext encrypted using an encryption scheme such as public key cryptography or common key cryptography requires a particular decryption key (see Non-patent literature 1, for example). In one of existing methods for a first apparatus that does not have a decryption key to obtain a result of decryption of a ciphertext, a second apparatus that has a decryption key provides the decryption key to the first apparatus and the first apparatus uses the decryption key to decrypt the ciphertext. In another existing method for the first apparatus to obtain a result of decryption of a ciphertext, the first apparatus provides the ciphertext to the second apparatus and the second apparatus decrypts the ciphertext and provides the result of decryption to the first apparatus.